In the spinning of glass fibers, there has long been desired flood-free operation, that is, to prevent a condition known as "flooding" from occurring. Flooding is defined as the covering or wetting of a substrate, such as the tip plate, the orifice (or nozzle) plate or sidewall of a feeder with molten glass which disrupts the formation of glass fibers.
In order to attain flood-free operation, there have been proposed various methods and apparatuses. British Patent No. 763,160 discloses the use of a feeder having a plurality of orifices disposed in or near the vertex of a V-member bottom plate made of a platinum-gold alloy (gold content 3 - 6%) in place of a tip plate. On the other hand, British Patent No. 1,049,517 discloses the use of a bushing containing about 1000 - 1200 tips made of a platinum-gold alloy (gold content 10 - 50 %), wherein the wettability of platinum-gold alloys decreases as the gold content increases. British Patent No. 1,350,644 discloses the use of a feeder having a tip section made of a platinum-rhodium alloy (rhodium content 15 - 85%) containing an additional one or more metals, said alloy having increased contact angle. Contrary to the use of the bushing containing tips, the use of a tipless base plate made of a platinum-rhodium-iridium alloy is disclosed in British Patent No. 1,242,921. According to said British Patent No. 1,242,921, the base plate of a bushing has good non-wetting characteristics and the orifices in the tipless base plate can be more closely spaced than are the orifices in conventional tipped bushings. There have also been proposed materials having reduced wettablity for molten glass and suitable for making base plate for bushings in British Patent No. 1,318,201 (platinum-rhodium-gold alloys), French Patent No, 930,934 (graphite, and the like) and the like. It should be noted that these references are quite silent on a start-up operation after flooding occurs. Once flooding occurs it is very difficult to effect separation thereafter. So far as employing the methods and apparatuses of these references, the number of orifices or tips in the base plate or nozzle plate of a bushing has to be limited naturally in order to carry out continuous flood-free operation, which results in limited production of glass fibers.
In order to increase productivity of glass fibers, Strickland discloses in U.S. Pat. No. 3,905,790 the use of an orifice plate with a greater number of orifices therein, but the orifice plate used may be made of any alloy, wettable or non-wettable. According to Strickland, it is necessary to provide a temperature control for the creation and maintenance of the asymptotic geometry of the fiber forming cones formed at each orifice. In the Strickland process it is essential to direct a bulk flow of rapidly moving gas upwardly to the orifice area in the orifice plate to cool said cones to provide a stable cone formation and to maintain separation of cones thus preventing flooding. Further Strickland teaches various methods of start-up of the method of his invention, but these methods are complicated, much more difficult to control, time-consuming and costly since there is required the flow rate regulation either by temperature control of the orifice plate or direction of a steady flow of air to the plate, once flooding has occurred. There is no inventive idea in the Strickland patent to use positively useless flooded molten glass instead of the flow rate regulation.